CHARTS

Box and Whisker Plot

Depict Variation in Data by Quartiles

Box and Whisker Plots (or simply boxplots) are very useful plots in descriptive statistics to analyze groups of numerical data through a five-number statistical summary. Box and whisker plots help you to see the variance of data as well as potential unusual data points in a dataset called outliers. The box-plot is especially useful for indicating whether a distribution is skewed and for comparing between two sets of numerical data.

The five statistics summary that a box-whisker plot portray are:

  • Minimum Value : The smallest value in the data set
  • Second quartile(Q1) : The value below which the lower 25% of the data are contained
  • Median value : The middle number in a range of numbers
  • Third quartile(Q3) : The value above which the upper 25% of the data are contained
  • Maximum value : The largest value in the data set

If outliers are present, the whisker on the appropriate side is drawn to 1.5 * IQR rather than the data minimum or the data maximum. This way, outliers are not calculated into the statistics of the dataset and would not be recognized as the minimum/maximum. Small circles or unfilled dots are drawn on the chart to indicate where suspected outliers lie.